Characterization of the Caenorhabditis elegans UDP-galactopyranose mutase homolog glf-1 reveals an essential role for galactofuranose metabolism in nematode surface coat synthesis

Galactofuranose (Galf), the furanoic form of d-galactose produced by UDP-galactopyranose mutases (UGMs), is present in surface glycans of some prokaryotes and lower eukaryotes. Absence of the Galf biosynthetic pathway in vertebrates and its importance in several pathogens make UGMs attractive drug targets. Since the existence of Galf in nematodes has not been established, we investigated the role of the Caenorhabditis elegans UGM homolog glf-1 in worm development. glf-1 mutants display significant late embryonic and larval lethality, and other phenotypes indicative of defective surface coat synthesis, the glycan-rich outermost layer of the nematode cuticle. The glf homolog from the protozoan Leishmania major partially complements C. elegans glf-1. glf-1 mutants rescued by L. major glf, which behave as glf-1 hypomorphs, display resistance to infection by Microbacterium nematophilum, a pathogen of rhabditid nematodes thought to bind to surface coat glycans. To confirm the presence of Galf in C. elegans, we analyzed C. elegans nucleotide sugar pools using online electrospray ionization-mass spectrometry (ESI-MS). UDP-Galf was detected in wild-type animals while absent in glf-1 deletion mutants. Our data indicate that Galf likely has a pivotal role in maintenance of surface integrity in nematodes, supporting investigation of UGM as a drug target in parasitic species.